Electric motors generally require two bearings. Ideally, the bearings used are as low cost as possible. Of the rolling bearing family, deep-groove ball bearings are generally the lowest cost. Axial flux motors do not ideally suit this kind of bearing because a large amount of axial (or thrust) load is present on one bearing within an axial flux motor due to the large amount of attractive force between the rotor and stator. The more common radial flux motor structure does not have this issue, the force being reasonably balanced within the structure and thus not substantially loading the bearings. The high thrust load in an axial flux motor can decrease bearing life substantially, and is a known issue with axial flux machine technology.
Deep-groove ball bearings typically require some minimum axial force to be applied in order to operate more quietly and have an increased lifetime, known as a “pre-load” force. However, the axial force produced in an axial flux motor can be very much greater than a recommended pre-load force. Indeed, the axial load placed on a deep-groove ball bearing in an axial flux motor can significantly reduce the lifetime of the bearing.
It would therefore be desirable to provide some means by which the thrust load on the bearing could be reduced, but retain enough force for sufficient pre-load. This would significantly increase the life of the bearing in an axial flux machine, and thus significantly increase the useful life of the product incorporating it.